A teacher attempting to assist his sister in their quiet Connecticut suburb when she believed she was being robbed shot a masked stranger during a late-night confrontation. But Jeffrey Giuliano, 44, didn't realize that he had gunned down and killed his teenage son until the boy was identified by authorities.

Police responding to a possible burglary attempt pulled up to a house in New Fairfield at 1 a.m. Thursday to find the local 5th grade teacher, dressed in a T-shirt and shorts, sitting on the lawn outside his sister's home (the two lived next door). Dead in the driveway was his 15-year-old son, Tyler.

Lieutenant J. Paul Vance said that Tyler was found with obvious gunshot wounds and was holding a weapon.

"We received a call reporting possible burglary and shots fired," Vance told ABC News. "He was shot multiple times, but we still don't know the number of times or the location."

Emergency Medical Service responders said that Tyler, who the Fairfield News Times reported was Giuliano's adopted son, was dead when they arrived on the scene.

Jeffrey Giuliano armed himself with a handgun and headed next door when he received a call from his sister, Alexis Scocozza, who suspected her home was being broken into.

Once he left his house, Giuliano immediately saw a masked person dressed all in black clothing and wearing a ski-mask and holding a "shiny object," according to the police report.

Giuliano, who teaches at the Meeting House Hill School in New Fairfield, told police that the masked stranger came at him with the object still in his hand and in a threatening manner. Giuliano said he believed that the stranger was armed, and during the confrontation that quickly followed discharged his handgun.

Police have not stated whether the object Tyler was holding at the time of the shooting was a weapon.

It was unclear how many times the teen was shot and where, Vance told ABC News. He said that the medical exam will be doing autopsy today, which be able to help out with the investigation.

"We're working out the timeline with the evidence and interviewing the witnesses and will figure out the timeline," Vance said. "We're going to examine everything and try to understand exactly how and why this occurred."

Police said that they have now determined whether the gun was registered to Jeffrey Giuliano but said they will not yet be releasing the details. Detectives were still processing the scene early Friday for physical and forensic evidence.

No charges have been filed against Giuliano. Calls made to his home by ABC News were not immediately returned.

Superintendent of New Fairfield schools Alicia Roy sent an email out to parents Thursday afternoon regarding the shooting.

"Our district has experienced a tragedy that has affected us deeply," she wrote, according to the News-Times. Roy said that the shooting was not discussed with students because "the facts were not clear."

Classmates of Tyler's took to Twitter to express their shock and grief at losing someone they've known for most of their lives.

"Never going to forget that laugh he had," Nick Cesarski wrote. "Weird to think a kid I knew since kindergarten is gone. He always was a good kid. R.I.P Tyler."